The invention relates to an optical transmitting and receiving device according to the preamble of patent claim 1.
In the case of an optical transmitting and receiving device, a transmission fiber must be coupled to a transmitting element, commonly a laser diode, and to a photodiode as receiving element. In the transmission fiber, the transmitted and received signals are transmitted simultaneously in the opposite direction. In the case of the same wavelength, the transmitted and received signals are separated by a beam splitter and, in the case of different wavelengths, are separated by a wavelength selective brancher. In order to obtain the lowest possible coupling losses, the fiber must be coupled both to the laser diode and to the receiving diode in an optimum fashion. In order to couple a laser to a monomode fiber, a beam transformation has to be carried out because of the different beam characteristics of both. For this purpose, imaging using one Or two lenses is normally used. The necessary magnification M is about three to five, according to the ratio of the mode field diameter of laser and fiber. Tolerances in the position of the laser are compensated by an active adjustment of the fiber. In the lateral direction, that is to say transverse to the beam direction, the adjustment range necessary for this is greater by the factor M than the lateral tolerance range of the laser and, in the axial direction, it is greater by the factor M.sup.2. The adjustment of the fiber in relation to the laser also influences the adjustment of the fiber in relation to the photodiode, so that in particular a small-area photodiode that is suitable for relatively high frequencies must likewise be actively adjusted in relation to the fiber.
DE 39 14 835 C1 discloses an arrangement for coupling an optical waveguide to an optical transmitting or receiving element.
Adjustment in the plane lateral to the optical axis is achieved by fixing the optical waveguide and optical transmitting or receiving element on different carriers which lie with their carrier surfaces on one another in a displaceable manner, and by the beam of light passing from the optical waveguide to the optically active element or vice versa by means of twofold reflection at each mirror plane located on a carrier. By displacing the carrier, a lateral adjustment is carried out. The carrier that carries the transmitting or receiving element can comprise a substrate and a part fitted thereon which has a continuous opening through which the beam of light passes. Application of the arrangement is possible in all transmission systems having optical waveguides, and in duplexers having input or output coupling of light. For the case of coupling to a transmitting element, a receiving element can be provided on the carrier with the fiber.